Medium Access Control Discard Notification

ABSTRACT

A method is provided for a base station set (NODE B) adapted for RLC and MAC-hs signaling in acknowledged mode (AM), the base station set at least forwarding protocol data units (MAC-d PDU) from a Radio Network controller (RNC) to a user entity (UE), the method comprising the steps of monitoring ( 1 ) the MAC layer of the transmission entity of the base station set ( 1 ), if a MAC discard has occurred in the MAC layer ( 3 ), that is, protocol data units (PDU&#39;s) have been deleted in the input buffer of the base station set (NODE B), transmitting ( 7 ) a discard notification message from the MAC transmission entity in the base station set to the RLC layer of the radio network controller (RNC), indicative of the discarding of protocol data units. There is moreover provided a method for a radio network controller (RNC) adapted for RLC and MAC-hs signaling in acknowledged mode (AM) and a method for a user entity (UE) adapted for RLC and MAC-hs signaling.

FIELD OF THE INVENTION

The present invention relates to packet data traffic and signalingbetween a user entity (UE), a radio base station (Node-B) and a radionetwork controller (RNC). More particular the invention pertains toHSPDA (High Speed Packet Data Access) traffic making use of among othersthe MAC-hs (Medium Access Control High Speed) and RLC (Radio LinkControl Layer) data transmission protocols.

BACKGROUND OF THE INVENTION

HSPDA provides high speed downlink access from an UMTS base station(Node B) to a plurality of user entities by flexible allocation ofdownlink resources.

In prior art document WO2005/03418 FIG. 3, the protocol layers involvedin the communication between user entity (e.g. mobile station), Node B(base station), RNC (implemented by parts CRNC, and SRNC) has beenshown. The user entity involves the following layers: PHY (physicallayer), MAC-hs (HSPDA Media Access Control layer), MAC_d (Medium AccessControl Device) RLC (Radio Link Control layer). Node B communicates viathe MAC-hs layer with the user entity and via a frame protocolHS_DSCH-FP with the RNC, respectively.

According to the HSPDA specifications, the RLC operates above the MAC-hsprotocol in the protocol stack. The RLC layer provides the connection toupper communication layers such as TCP/IP, both in the user entity andthe RNC. Both the RLC protocol and the MAC-hs protocol are ARQ(Automatic Repeat Request) protocols featuring retransmissions ofincorrectly received protocol data units.

As the name implies, the High Speed Downlink Packet Access (HSDPA)technology introduced in 3GPP provides substantial data capacityadvantages. The technical specification 3GPP TS 25.321 concerns the MAC(Media Access Control) architecture and the various entities form afunctional point of view. 3GPP 25.211 basically describes howinformation from the MAC-layers is mapped onto the channels sent out onthe air.

In contrast with release 99 (GSM/EDGE) which exclusively defineschannels between the RNC and the UE, HSPDA introduced the HS-DSCH (HighSpeed Dedicated Shared Channel) channel which are terminated between theuser entity and the base station set (NODE B) also denoted Node B. TheHSPDA Medium Access Control (MAC-hs) enables increased packet datathroughput due to link adaptation (Adaptive Modulation Coding—i.e.16 QAMor QPSK) and fast physical layer retransmission combining. Hence,besides incorporating the WCDMA access technology, Node B carries outscheduling and Hybrid Automatic Repeat Request (H-ARQ) retransmissionson the channel between the user entity and Node B. The benefits and thefeatures of the above system have for instance been described in “WCDMAevolved—High Speed packet data services”, by Stefan Parkwall et al.,Ericsson review No. 2, 2003.

The HSPDA transmission makes use of a 2 ms transmission time interval(three time slots).

On the downlink side there is provided: Several common data channels 1,a Downlink Physical Channel (DPCH—R99) dedicated signal radio bearer 2for each user entity using HSPDA transmissions; a common High SpeedShared Control Channel (HS-SCCH) for control signalling 3, a number ofHigh Speed—Physical Downlink Shared Channels (HS-PDSCH) common user datachannels 4-5, which are allocated HSPDA data in a flexible manner.

On the uplink side there is provided: a High Speed—Dedicated PhysicalControl Channel (HS-PDCCH) 6—for, among other things, providing channelquality information, CQI, and HSPDA automatic request signalling—and anuplink dedicated channel associated with each HSPDA user comprisingcontrol information and data, 7.

HSDPA (High Speed Downlink Packet Access) facilitates high speedtransmission on the downlink from Node-B and to the user entity (UE).Under HSPDA, Node-B buffers incoming downlink end-user data and utilisesan internal scheduling entity to determine on which particular channeland when to transmit buffered data according to a scheduling routine. Toaim in the scheduling decision, Node-B continuously receives channelquality estimates from the UE entities. Node-B also has knowledge aboutUE receive capabilities.

Node-B can transmit MAC-hs PDUs (Media Access Control High SpeedProtocol Data Units) to the UEs at a pace of up to 500 times per second.At each 2 ms transmit opportunity (TTI transmit time interval) Node-Bcan vary the MAC-hs PDU size depending on the buffered amount of data,the channel quality estimates, the UE capabilities and the grantedamount of downlink codes available. MAC-hs data for 1 UE up to 4 UEs canbe scheduled at each 2 ms transmit opportunity utilising code division(WCDMA) among the scheduled UEs.

The UE decodes the HS-SCCH (High Speed Shared Control Channel), and upona successful CRC checksum the UE continues to decode the HS-PDSCH (HighSpeed Physical Data Shared Channel). Depending on the outcome of theHS-SCCH and HS-PDSCH, the UE transmits a reception feedback back to thepeer Node-B.

The reception feedback is interpreted by the Node-B transmitter, whichupon a negative feedback or absence of feedback (DTX) indicating apossible reception failure for the UE, retransmits data.

According to specification 3GPP 25.321 chapter 11.6.1 and 11.6.2, thereis utilized a HSPDA N-channel stop and wait (SAW) ARQ, implying that anumber of 1-8 HARQ processes may exist at a time per user entity. Thetiming relation between the downlink HS-DPCCH channel and the uplinkACK/NACK transmissions on the HS-PDSCH are fixed, that is, the ACK, NACKmessages are arranged to be transmitted, such that there are always7,5-9,5 TTI slots between a transmission and the associated expectedACK/NACK from a user entity. This allows for Node-B to easily determinewhen to retransmit data in the case of a missing response to a firsttransmission. The 8 HARQ processes mentioned above corresponds to thenumber of downlink transmissions to a given entity which can beaccomplished before the NACK/ACK pertaining to the first downlinktransmission is received at the base station.

Base Station and User Entity

In FIGS. 12 and 13, diagram of a base station set (Node B) and a userentity (UE), respectively, are shown.

The base station set, node B, comprises a MAC-hs control messagehandler, a scheduler, a number of input buffers storing segments of datastreams pertaining to individual user entities, UE1-UEn, correspondingto a number of HARQ processes for handling simultaneous transmissions toseveral UE's, that is, for each user entity as well, Layer 1 processingmeans for transferring data from respective HARQ processes. The basestation moreover comprises a CQI decoder, a user entity (UE) feedbackdecoder and a layer 1 receiver.

Each HARQ process in a given user entity is mirrored in Node B, andcorresponds to a given data stream which is received by a particularuser entity. As explained above, more data streams may be used by theuser simultaneously corresponding to one application or moresimultaneous applications running on the user entity apparatus, possiblywith different QoS requirements. Moreover, consecutive data may betransmitted for the same user entity, the consecutive transmissionbelonging to different HARQ processes.

Moreover, Node B comprises at least one specific input buffer queuededicated to a corresponding set of HARQ processes.

In FIG. 13, a user entity (MAC) arrangement according to the inventionis shown comprising HS-SCCH decoding means, for decoding the downlinkHD-PDSCH channel, arrangements consisting of a number J of HARQprocesses, a number N of reordering and disassembly queues and a RLC(Radio Link Control) layer means. Moreover, there is provided UE (UserEntity) feedback processing means and layer 1 processing for providingfeed-back on the HS-DPCCH channel.

The reordering queue distribution function routes the MAC-hs PDU's tothe correct reordering buffer based on a Queue ID. The reordering entityreorders received MAC-hs PDU's according to the received TSN (transmitsequence number). MAC-hs PDU's with ascending TSN's (MAC hs TransmitSequence Numbers) are delivered to the disassembly function. To recoverfrom erroneous conditions when MAC-hs PDU are missing the same avoidancehandling as described in 3GPP TS 25.321-11.6.2, re-ordering releasetimer and window based stall avoidance, shall be used. There is onereordering entity for each Queue ID configured at the UE. Thedisassembly entity is responsible for the disassembly of MAC-hs PDU's.When a MAC-hd header is removed, the MAC-d PDU's are extracted and anypadding bits are removed. Then the MAC-d PDUs are delivered to thehigher (RLC) layer. These features have been described in 3GPP TS25.321-11.6.2.3.

The RLC Layer

The RLC layer in 3GPP can operate in three modes, transparent mode,unacknowledged mode and acknowledged mode (AM), which will be focusedupon in the following.

In AM mode, incorrectly received PDU's (Protocol Data Units) discoveredby the receiving side are effected to be retransmitted by thetransmitting side by means of an ARQ (Automatic Repeat Request)protocol.

An AM RLC entity consists of a transmitting side, and a receiving side,where the transmitting side of the AM RLC entity transmits RLC PDU's andthe receiving side of the AM RLC entity receives RLC PDU's.

An AM RLC entity resides in the UE (user equipment) and in the RNC(radio network control), respectively. The transmitting side segmentsand/or concatenates RLC SDU's (service data units) into PDU's of a fixedlength. The receiving side reassembles received PDU's into RLC SDU's andtransmits these to higher data layers. Likewise, SDU's are received fromthe layer above the RLC layer. In AM mode, the RLC layer is responsiblefor the delivery of SDU's in consecutive order.

In FIG. 4 of the above document WO2005/034418, an implementation of theacknowledged mode (AM) UE (base station)/UTRAN (Radio access node/basestation (Node B)) entity is shown.

To facilitate the in-sequence delivery, each RLC PDU is given a sequencenumber, 0-4095, whereby the transmitter transmits PDU's with increasingsequence number modulo 4096. Using the sequence number, the receiver candetect a missing PDU. The receiver can be configured to transmit aSTATUS message upon the detection of a missing PDU. The STATUS reportmay contain positive or negative acknowledgement of individual RLC PDU'sreceived by the peer RLC entity. The transmitter can also request aSTATUS messages from the receiver by setting a Poll flag in the PDUheader. The conditions for that the transmitter sets the Poll flag areamong others:

Last PDU in Buffer.

When only one PDU exists in the input buffer.

Poll Timer Expires.

When the timer_poll expires, that is, the transmitter requested a STATUSearlier and initiated a timer_poll to reassure that a response isreceived.

Window Based.

A transmitter is restricted in the amount of “outstanding data” it cantransmit until a STATUS confirms the reception to the receiving side.“Outstanding data” relates to the earliest unacknowledged PDU.

Note that the above description of the functionality of the RLC layeronly constitutes a small excerpt of those features actually provided.

Selective retransmissions are possible, e.g. if STATUS message indicatesPDU with sequence number (SN) 3, 6 and 13 are missing, only 3, 6 and 13needs to be retransmitted.

MAC-hs Layer

In the following description regarding the MAC-hs layer:

-   -   the MAC-hs transmitter is the Node-B.    -   the MAC-hs receiver is the UE equipment being either a mobile        station or a pc-card attached to a PC or any other equipment        capable of receiving downlink 3GPP HSDPA traffic.

MAC-hs PDU's are numbered by modulo TSN (Transport Sequence Number)cycling through the field 0 to 63.

As mentioned above, the MAC-hs protocol provides multiple Hybrid-ARQprocesses (HARQ) whereby for each HARQ process, the transmittertransmits a MAC-hs PDU and awaits either an ACK indicative of receptionat the receiver or Negative Acknowledgement (NACK) indicative that thereceiver did not receive the MAC-hs PDU or absence of a response (DTX).The round trip time concerning the time from MAC-hs PDU transmissionuntil reception of the feedback (ACK/NACK) is fixed. Upon the receptionof a NACK or DTX, the MAC-hs transmitter retransmits the MAC-hs PDU.Since the round trip time is long in relation to the MAC-HS PDU size andsince multiple users may be adapted to receive packets in timemultiplexed fashion, multiple HARQ processes are provided. If only oneHARQ process was available, the duty cycle (i.e. actual transmissiontime/total possible transmission time) would be low. By using multipleHARQ processes, one HARQ process can await a response, while anotherHARQ process, or multiple HARQ processes, may transmit. Thereby, theduty cycle can be rendered close to 100 percent.

The MAC-hs protocol is semi-reliable, that is, the MAC-hs transmittermay choose to discard or delete a MAC-hs PDU that has been transmittedand possibly been retransmitted to the MAC-hs receiver.

By discarding a MAC-hs for retransmission, unnecessary transmissions areprevented over the radio link in case the MAC-hs receiver has moved toanother cell or has powered down or if the receiver for any other reasonis not capable of receiving data. Therefore, buffered packets arediscarded at the transmitter either at the expiry of a timer set at apredetermined time (e.g. T1) corresponding to the first transmission ofthe packet in question or when a maximum number of retransmissions ofthe packet in question have been performed or based upon a too longwaiting time in the input data buffer, whatever appears first or acombination thereof.

The MAC-hs receiver utilizes a receiver window for the purpose ofmitigating the effect of unnecessary transmissions when PDU's arereceived in non-ascending sequence order (which can occur due toretransmissions). Whenever a MAC-hs PDU is successfully received with aTSN (Transmit Sequence Number) equal to the next expected TSN, thereceiver can deliver PDU's to the RLC layer. Depending on whether thesubsequent TSN number (i.e. next expected TSN+1) has already beensuccessfully received, that MAC-hs PDU can also be delivered and soforth. The receiver window is updated accordingly. Delivery to the RLClayer from the MAC-hs protocol is done in consecutive order, alsodenoted in-sequence.

To recover from the situation where e.g. the transmitter has discarded aMAC-hs PDU, the receiver utilizes two mechanisms I)+II) to solve theproblem:

I) Timer Based Stall Avoidance:

At the reception of a PDU with TSN>next_expected_TSN the receiver startsa timer denoted T1. When the timer expires, the receiver makes properactions to allow for sub-sequent PDU's to be received. The exact detailsare described in 3GPP 25.321 Chapter 11.6.2.3.2. The behavior is shownin FIG. 1.

At time 1) a PDU with TSN=4 is received, the next expected transmitsequence number being 3, whereby timer T1 starts.

At time 2) PDU's with TSN 6 and 7 are received.

At time 3), the timer expires, whereby TSN=4 is delivered to the RLClayer. Next expected_TSN=5. A new timer T1 starts sincenext_expected_TSN=5 is not received and at least one PDU exists inreceiver window.

4) TSN 6 and 7 remains in buffer.

II) Window Based Stall Avoidance:

Upon the reception of a PDU with TSN outside the receiver window, thereceiver shall shift its “right” (or “upper”) window edge andhighest_received_TSN to the received TSN. Next_expected_TSN shall beupdated to highest_received_TSN—receiver window size+1I previously PDU'sstored in window that now fall outside the window shall be delivered toRLC layer. This has been illustrated in FIG. 2.

Assume that the receiver window size is of length 8.

At time 1) PDU TSN 4 has been received, which is within the receiverwindow, TSN=3 is next_expected_TSN, timer T1 is running.

At time 2) TSN=12 is received, which is outside the receiver window thuscausing the window to advance, the next_expected_TSN is updated, and PDUTSN=4 is delivered to RLC. A new timer T1 starts since next_expected_TSNis not received and a PDU exists in the receiver window.

MAC-hs Reset:

MAC-hs is used to restart the MAC-hs protocol, where the MAC-hs receiverdelivers stored data in its receiver window to RLC layer and sets itsnext_expected_TSN=0 and highest_received_TSN=63. It is used uponconditions such as handover between cells.

Problems with Existing Solutions

Assume the case when a TCP session is started from the fixed network toa peer user residing in a 3GPP HSDPA network having e.g. a pc-cardinserted in a laptop. The TCP transmitter at the fixed network starts bytransmitting very low amount of data. Assume further that the RLC layerresides in the Radio Network Controller (RNC) and that it transmits thedata to Node-B within 2 RLC PDU's. The two PDU's are first stored inNode-B incoming data buffer. FIG. 3 shows the situation.

Assume moreover, that Node-B transmits both RLC PDU's in one MAC-hs PDUwith TSN=0. Assume now that the transmission fails and Node-B repeatstransmission of the PDU until it is finally discarded at the Node-B.Node-B then advances its window to sequence number 1 as its BoW (Bottomof Window). FIG. 4 shows the situation.

When subsequently the RLC poll timer expires and RLC retransmits thelast RLC PDU (TSN=46). Node-B will receive the RLC PDU data, andtransmit the data in one MAC-hs PDU to UE. Assume successful receptionoccurs. UE will start its T1 timer since receivedTSN<>next_expected_TSN.

It is assumed that the time from the first transmission in Node-B untilNode-B discards a MAC-hs PDU is shorter than Poll_timer to avoid thatduplicate RLC PDU's are buffered in Node-B. FIG. 5 shows the situation.

If we now assume that T1 timer in MAC-hs receiver<Poll timer in RLC,subsequently the T1 timer in UE will expire and the PDU will be receivedby RLC receiver (RLC TSN=46). RLC receiver in UE will transmit a STATUSmessage indicating the absent RLC PDU with TSN=45. RLC transmitter willthen retransmit RLC PDU with TSN=45 and upon successful reception at theUE MAC-hs receiver RLC layer can deliver RLC PDU's 45 and 46 to higherlayer.

An other scenario can occur if T1 timer in MAC-hs receiver>Poll timer inRLC then yet another RLC PDU 46 will be sent—but since T1 timer is stillrunning nothing will be sent to RLC receiver until T1 expires. When T1expires in the UE multiple copies of TSN 46 will be received by the RLCreceiver.

As described above, the UE will now send a STATUS indicating the absenceof TSN=45, and upon the reception of the STATUS message in RLC, the RLCwill retransmit the TSN=45. If we assume successful delivery of the RLCPDU with TSN=45 via the MAC-hs layer the UE RLC layer can now deliverthe complete data sequence TSN=45 and 46 to its upper layer.

We can conclude that the delay until the PDU's are correctly received atthe RLC receiver is Poll_timer+RLC PDU transmit time from RLC in RNC toMAC-hs in UE+T1 timer in UE+STATUS control message UL transmit time fromUE to RLC+RLC PDU transmit time from RLC in RNC to RLC in UE.

For the case of a higher traffic load, e.g. when TCP is running at highspeed, the problem will be less noticeable, because the UE will morelikely start its T1 timer because more transmission occurs betweenNode-B and UE. For a high load traffic case, either the 1st (timerbased) or 2nd (window based) recovery mechanism will cause Ue to deliverdata to RLC. If configured to transmit STATUS upon missing PDU's, the UEwill send a STATUS. The transmit RLC entity will then receive a STATUSmessage prior to that the poll_timer expires.

In conclusion, where two ARQ (Automatic Repeat Request) in-sequencedelivery protocol layers operate in the same protocol stack, and whenthe underlying ARQ protocol discard data, the above problem of datadelay, as seen by the application operating above the two ARQ protocols,can occur. If the problem occurs during low traffic load situations itmay cause a relatively long delay until an automatic resolution occurs.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a prior art T1 timer based stall avoidance,

FIG. 2 shows a prior art window based stall avoidance,

FIG. 3-5 shows a problem associated with a possible known scenario inthe prior art,

FIGS. 6 a+6 b shows an exemplary scenario according to the invention,

FIG. 7 shows a first comparative prior art scenario,

FIG. 8 shows a second comparative prior art scenario,

FIG. 9 shows a flow diagram pertaining to a first, second and thirdembodiment of the invention,

FIG. 10 shows a flow diagram pertaining to a second embodiment of theinvention,

FIG. 11 shows a flow diagram pertaining to a fourth embodiment of theinvention,

FIG. 12 shows a base station according to the invention, and

FIG. 13 shows a user entity according to the invention.

SUMMARY OF THE INVENTION

It is a first object of the invention to obviate the time lag which mayoccur in systems having two protocol layers, each respective layeroperating in accordance with acknowledge/non acknowledge signaling.

This object has been accomplished by the method set forth for a basestation set (NODE B) adapted for RLC and MAC-hs signaling inacknowledged mode (AM), the base station set at least forwardingprotocol data units (MAC-d PDU) from a Radio Network controller (RNC) toa user entity (UE), the method comprising the steps of monitoring (1)the MAC layer of the transmission entity of the base station set, if aMAC discard has occurred in the MAC layer, transmitting a discardnotification message from the MAC transmission entity in the basestation set to the RLC layer of the radio network controller (RNC),indicative of the discarding of protocol data units.

The above object has also been accomplished by a method for a basestation set (NODE B) adapted for RLC and MAC-hs signaling, the basestation set communicating with a user entity and a Radio Networkcontroller in acknowledged mode, the method comprising the steps ofmonitoring the MAC layer of the transmission entity of the base stationset, if a MAC discard has occurred in the MAC layer, transmitting aMAC-hs_b reset message to the MAC receiver of a user entity.

This object has moreover been accomplished alternatively by a userentity adapted for RLC and MAC-hs signaling, in which a Radio Networkcontroller at least forwarding protocol data units to a base station setfor further forwarding to the user entity the method comprising thesteps of when receiving a MAC-hs_b RESET message, resetting nextexpected transmit sequence number (TSO) to 0, resetting thehighest-received transmit sequence number to 63, delivering all receivedRLC protocol data units (PDU) to the RLC layer of the user entity,transmitting an acknowledge message to the base station.

Additional advantages will appear from the following detaileddescription of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

According to the present invention, various solutions are set forth fordiscovering when the above problem associated with the prior art occursand for providing explicit signaling to recover faster from theerroneous situation.

Embodiment 1

According to a first embodiment of the invention in order to mitigatethe effect of the data discarding discussed above, Node-B indicates upto the RLC layer that a PDU discard has appeared with a Node-B discardnotification message. This notification takes place when Node-B performsa discard of MAC-hs PDU(s). According to the invention, the signalingmay take place as a new IE (Information Element) in an existing controlmessage in uplink direction, or as a new control message. Following thereception of the discard notification, the RLC transmission entitydecides what action to take.

In FIG. 9, a flow diagram pertaining to the procedure carried out inNode B is illustrated.

In step 1, node B monitors the MAC layer in acknowledged mode of thetransmission entity.

If a MAC discard has occurred in the MAC layer in the AM transmissionentity, step 3, node B proceeds directly to step 7 wherein the MAC layerof node B transmits a Discard notification message to the RLC layer ofthe RNC, indicating that a MAC discard occurred in the MAC layer.

Optionally, in step 7, the Discard notification message comprises asignaling of the amount of data discarded, and also optionally comprisesthe RLC sequence numbers of the discarded PDU's in question.

Subsequently, the RLC transmission layer entity in the RNC acts on thediscard notification, step 8, whereby the RNC transmission entityperforms at least one of the following steps:

A) Ignore the Discard notification and continue to transmit data fromthe input buffer—if more date is present in the input buffer. If no datais present in the input buffer, the RNC may also ignore the Discardnotification. This means that the RNC relies on existing higher layerprotocols for retransmission of missing PDU's or may also be due toabsence of handling means for the Discard message,

B) transmitting all outstanding RLC PDU's, that is, re-transmitting alltransmitted but non-acknowledged PDU's and set the poll bit on the lastPDU,

C) re-transmitting PDU's with sequence number optionally included in theDiscard notification with the poll bit set on the last PDU,

D) re-transmitting a single RLC PDU (highest transmitted sequence number(SN)) with the poll bit set or without the poll bit set if pending RLCPDU's awaits transmission,

E) invoking a MAC-HS reset, which will cause the MAC-hs receiver todeliver data to RLC receiver.

Embodiment 2

In FIG. 10, a second embodiment of the invention is shown.

According to a second embodiment of the invention, having steps of thesame reference numbers in common with the first embodiment, thefollowing procedure is carried out:

In step 1, node B monitors the MAC layer in acknowledged mode of thetransmission entity.

If a MAC discard of a MAC-d PDU occurs in the input buffer in Node-Bi.e. a transmission to the UE has not occurred yet of this MAC-d PDU,step 2, the procedure goes to step 7, otherwise it goes to step 3.

In step 3, it is tested if a MAC discard has occurred in the MAC layerin the acknowledged mode entity, if no the procedure goes to step 1, ifyes the procedure proceeds to step 4.

In step 4, it is examined if an acknowledge (ACK) has been received forMAC-HS with transmit sequence number (TSN) larger than the transmitsequence number of the discarded MAC-hs PDU but within senders transmitwindow. If no, proceed to step 5, if yes proceed to step 6. It is notedthat the reason for not transmitting the discard notification, as willbe the effect when moving to step 6 from step 4, is due to the fact thatthe UE has started its T1 timer, and that the UE will inform the RLClayer of the missing PDU upon the expiration of the T1 timer.

In step 5 it is examined if there are pending MAC-HS transmissions ordata in the input buffer. If yes proceed to step 6, if no proceed tostep 7. It is that the reason for proceeding to step 6 from step 5 l isdue to the fact that Node-B will generally transmit MAC-hs in ascendingTSN number order. Prior to a transmit attempt of a MAC-hs for an UE,Node-B will try to select lowest possible TSN in Node B transmit window.This means that if a discard occurs for e.g. TSN=n, it is not likelythat Node-B has pending MAC-hs transmissions for TSN<n. Likewise, ifreceived but not yet transmitted MAC-d PDU's occur these PDU's will besent with TSN>n. As will be appreciated by those skilled in the art, TSNis counted modulo 64 which must be taken into account in the examplegiven above.

In step 6, no discard notification is transmitted.

In step 7, a MAC layer transmit discard notification to the RLC layer istransmitted, informing that a Discard occurred, and optionally includingthe amount of data discarded. The procedure continues in step 8, shownand described under step 8 in FIG. 9, such that Node-B will according tothe second embodiment of the invention transmit the Node-B discardnotification message in the same manner and with the same subsequentsteps as explained above.

Compared to the first embodiment this embodiment, the second embodimentof the invention reduces the signaling between Node-B and the RNC.

Embodiment 3

To help the transmit RLC entity in its decision, the Node-B discardnotification message comprises the amount of data discarded by theNode-B. Alternatively, by investigating the MAC-d PDU, Node-B can decodethe RLC sequence number and specify the discarded sequence numbers.

This option has been indicated in FIG. 9 in step 7. The RNC can, byusing this information, estimate which RLC PDU's that requireretransmission, or, if the RLC sequence numbers are provided retransmitonly those PDU's that were discarded.

Embodiment 4

An alternative MAC-hs reset is defined as a control message that can betransmitted from the Node-B, denoted MAC-hsb_reset. This procedure isillustrated in FIG. 11. The user entity UE is the receiver and Node B isthe transmitter.

In step 401, the MAC layer in the AM transmission entity is monitored.

If a MAC discard occurs, step 402, in the MAC layer, the MAC transmitterentity transmits a MAC-hsb_reset message according to the invention tothe MAC-hs user entity receiver, step 403. The message is transmitted tothe user entity UE from Node-B. Otherwise the procedure goes to step401.

Upon reception of the MAC-hsb_reset, 404, the MAC-hs receiver shallreset its next_expected_TSN to 0 and highest-received_TSN to 63 anddeliver all received RLC PDU's up to RLC layer, 405. The MAC-hsb_resetmessage shall subsequently be acknowledged by the user entity UE, 406.

Upon reception of the acknowledgement 407, the MAC-hs transmitter shallset its transmitter BoW to 0, step 408.

The transmitter shall repeat the message upon a negativeacknowledgement, cf. step 404, to reassure that the receiversuccessfully receives the message. During the MAC-hsb_reset transmissionand time until an acknowledgement is received, no other transmissionsshall occur. This is to avoid any ambiguities of the TSN interpretation.

The MAC-hsb_reset may also be used periodically during time when no datais transmitted for the particular UE. This may be used to ensure thattransmitter and receiver has the same interpretation of BoW.

Comparison of the Present Invention with the Prior Art Under ExemplaryScenariosFIGS. 6 a+6 b

In FIGS. 6 a and 6 b, an exemplary handshake diagram according to thefirst embodiment of the invention is shown pertaining to an exemplaryscenario in which the following steps occur/are carried out:

101) A small amount of data is received at the RNC for a particularuser. (E.g. Assume the user starts a downlink TCP session towards the UEand TCPs speed is about to ramp up.)

102) RNC transmits the received data in two MACd PDU's to Node B withsequence number 45 and 46. RNC sets the POLL FLAG on the last sent PDU(SN 46) to reassure that either a) data is correctly received at the UEor b) if delivery fails, the RNC will trigger a retransmission when thePOLL FLAG timer expires.

103) NODE B transmits data in a single MAChs PDU with TSN=0.

104) NODE B retransmits data due to a NACK (or no response [DTX]) fromthe UE. NODE B continues with this step until step 105 occurs.

105) Node-B Discards the MAChs PDU with TSN=0, since the T1 timerexpires corresponding to step 2, FIG. 9.

112) Node B transmits a DISCARD notification to the RNC according tostep 5, FIG. 9.

120) the DISCARD notification is received by the RLC layer of the RNC,which subsequently transmits PDU with SN=46 and restarts POLL FLAGtimer, corresponding to option D, step 6, FIG. 9.

Note, that as an alternative, the RNC could retransmit both SN=45 andSN=46. With this approach, the steps from and including step 140) andabove could be avoided (see below).

125) Node B receives the MAC-d PDU from RNC and transmits in one MAC-hsPDU with TSN=1. UE receives data and sends an ACK, but since UE expectsTSN=0 it will start its T1 timer to allow NodeB to retransmit TSN=0(which will not occur in this example).

130) the T1 timer expires in UE MAC-hs. Next_expected_TSN is set to 2and highest_received_TSN is set to 1. After reassembly of TSN=1 the datais delivered to RLC.

135) the RLC at the UE transmits a STATUS message identifying SN=45 asmissing and SN=46 as received.

140) the RLC at the RNC receives STATUS, and retransmits SN=45 andrestarts the POLL FLAG timer.

145) Node B receives the MAC-d PDU from the RNC and transmits a MAC-hsPDU with TSN=2. UE receives data and sends an ACK. Data is delivered toRLC. 150) the RLC layer at the UE transmits STATUS message identifyingSN=46 as the highest received sequence number. The STATUS message may bearranged in various ways: For instance, the STATUS may indicate that upto a given sequence number everything is correctly received. The STUTUSmessage may also be formed as a bitmap indicating received andnon-received sequence numbers.

At reception of the STATUS message, the RLC at the RNC stops the POLLFLAG timer.

155) After reassembly, the RLC at the UE delivers the RLC SDU to theupper layer.

FIG. 7 Scenario

In FIG. 7, an exemplary handshake diagram according to the prior art isshown pertaining to an exemplary scenario comprising the followingsteps:

201) A small amount of data is received at the RNC for a particularuser. (E.g. Assume the user starts a downlink TCP session towards the UEand TCP's speed is about to ramp up.)

202) RNC transmits the received data in two MACd PDU's to Node B withsequence numbers 45 and 46. RNC sets the POLL FLAG on the last sent PDU(SN 46) to reassure that either a) data is correctly received at the UEor b) if delivery fails, the RNC will trigger a retransmission when thePOLL FLAG timer expires.

203) NODE B transmit data in a single MAChs PDU with TSN=0.

204) Subsequently, transmission and retransmission(s) are attempted—butstill failure on the air interface.

205) Node-B Discards the MAChs PDU with SN=0

206) time passes

207) POLL FLAG timer expires in the RNC. The RNC can now a) retransmit45 and 46 and set PF (Poll Flag) on last sent PDU (SN=46) or b) sendlast PDU with PF set (SN=46).

b) is shown in FIG.

208) Transmission by Node B is successful, but since UE expects TSN=0 itwill start its T1 timer to allow NodeB to retransmit TSN=0.

209) time passes, but probably not so long as the previous timer (206)

210) T1 timer expires and Next_Exp_TSN=2, highest received TSN=1 andreceived data is sent to RLC.

211) the UE RLC transmits STATUS indicating SN=45 as missing and SN=46as received.

213) SN 45 is retransmitted by the RNC

It is noticed that according the invention, the time lags 206) and thetime to execute 211 and 213 are avoided which otherwise would appearrespectively between steps 205)-207). The time saving corresponding tolag 206) occurs since progress will not depend on the expiry of the RNCpoll flag timer.

FIG. 8 Scenario

The scenario of FIG. 8 is similar to but differs from FIG. 7 in that RNChappens to receive more data, cf. 307), while it is waiting for theacknowledgement of SN 45, 46.

This scenario will recover faster than the scenario shown in FIG. 7,since the POLL FLAG Timer waiting time is avoided. Compared to FIGS. 6a+6 b the delay will be the same if we assume step 307) occurs at thesame time as 120) 1 FIGS. 6 a+6 b.

If the RNC in step 120) instead retransmitted both SN=45 and SN=46 theperiod 312) of FIG. 8 can be avoided according to the present invention.

At the time of X-step 305), the invention will send a discardnotification indicating that 45, 46 were discarded. Steps 301-313correspond largely to steps 201-213 above.

1. A method for a base station set (NODE B) adapted for RLC and MAC-hssignaling in acknowledged mode (AM), the base station set at leastforwarding protocol data units (MAC-d PDU) from a Radio Networkcontroller (RNC) to a user entity (UE), the method comprising the stepsof: monitoring the MAC layer of the transmission entity of the basestation set; and if a MAC discard has occurred in the MAC layer,transmitting a discard notification message from the MAC transmissionentity in the base station set to the RLC layer of the radio networkcontroller (RNC), indicative of the discarding of protocol data units.2. The method according to claim 1, wherein the discard notificationcomprises information of the amount of data discarded.
 3. The methodaccording to claim 1, wherein the discard notification comprises the RLCsequence numbers (SN) of the data discarded.
 4. The method according toclaim 1, wherein if a MAC discard of data in the input buffer has notoccurred, but a MAC discard has occurred in the MAC layer in theacknowledge mode entity and an acknowledge has been received for MAC-hswith a transmit sequence number (TSN) larger than the discarded transmitsequence number or if there are pending MAC-hs transmissions or data inthe input buffer refraining from sending a discard notification.
 5. Amethod for a radio network controller (RNC) adapted for RLC and MAC-hssignaling in acknowledged mode (AM), the Radio Network controller (RNC)at least forwarding protocol data units (MAC-d PDU's) to the basestation set (NODE B) for further forwarding to a user entity (UE), themethod comprising the steps of when receiving a notification Discardmessage performing at least one of the steps of: A) continuingtransmitting data; B retransmitting all outstanding RLC protocol dataunits; C) Retransmitting protocol data units whose sequence numbers havebeen provided in the discard notification; D) retransmitting a singleRLC protocol data unit with or without the poll bit set; and, E) the RLClayer invoking a MAC-hs-reset operation.
 6. A method for a base stationset (NODE B) adapted for RLC and MAC-hs signaling, the base station setcommunicating with a user entity (UE) and a Radio Network controller(RNC) in acknowledged mode (AM), the method comprising the steps of:monitoring the MAC layer of the transmission entity of the base stationset; and, if a MAC discard has occurred in the MAC layer, transmitting aMAC-hs_b reset message to the MAC receiver of a user entity.
 7. Themethod according to claim 6, wherein upon subsequently receiving anacknowledge message from the user entity (UE), reset all HARQ processesand set TSN on next transmission to 0 in the base station for the givenuser entity.
 8. A method for a user entity adapted for RLC and MAC-hssignaling, in which a Radio Network controller (RNC) at least forwardingprotocol data units (MAC-d PDU's) to a base station set (NODE B) forfurther forwarding to the user entity (UE), the method comprising thesteps of: when receiving a MAC-hs_b RESET message, resetting nextexpected_transmit sequence number to 0, resetting the highest-receivedtransmit sequence number to 63, delivering all received RLC protocoldata units to the RLC layer of the user entity, and, transmitting anacknowledge message to the base station.
 9. A base station set adaptedfor RLC and MAC-hs signaling in acknowledged mode (AM), the base stationset at least forwarding protocol data units (MAC-d PDU) from a RadioNetwork controller (RNC) to a user entity (UE), the base stationDeforming the operations of: monitoring the MAC layer of thetransmission entity of the base station set, and if a MAC discard hasoccurred in the MAC layer, transmitting a discard notification messagefrom the MAC transmission entity in the base station set to the RLClayer of the radio network controller (RNC), indicative of thediscarding of protocol data units.
 10. A radio network controller (RNC)adapted for RLC and MAC-hs signaling in acknowledged mode (AM), theRadio Network controller (RNC) at least forwarding protocol data units(MAC-d PDU's) to the base station set (NODE B) for further forwarding toa user entity (UE), the radio network controller when receiving anotification Discard message performing at least one of the steps of: A)continuing transmitting data, B retransmitting all outstanding RLCprotocol data units; C) Retransmitting protocol data units whosesequence numbers have been provided in the discard notification; and, D)retransmitting a single RLC protocol data unit with or without the pollbit set E) the RLC layer invoking a MAC-hs-reset operation.
 11. A userentity (UE) adapted for RLC and MAC-hs signaling, in which a RadioNetwork controller (RNC) at least forwarding protocol data units (MAC-dPDU's) to a base station set (NODE B) for further forwarding to the userentity (UE) the user entity, when receiving a MAC-hs_b RESET message,performing the operations of: resetting next expected_transmit sequencenumber (TSO) to 0, resetting the highest-received transmit sequencenumber (TSN) to 63, and delivering all received RLC protocol data units(PDU) to the RLC layer of the user entity (UE), transmitting anacknowledge message to the base station (NODE B).